Shining light on Pr³⁺-doped Bi₄(SiO₄)₃ phosphors for wide-range high-temperature luminescent thermometers

Non-contact optical thermometer has been propelled to the frontiers of research due to its non-invasive operation, high thermal sensitivity, and fast response. Herein, a novel, to our knowledge, class of Pr³⁺-doped Bi₄(SiO₄)₃ (BSO) phosphors was developed to achieve advancing fluorescent ratiometric thermometry: having a maximum relative sensitivity (S_r) of ~3.54% K^-1 at 298 K, and sustaining an entire S_r value beyond 1.59% K^-1 over the range of 298-468 K. The intriguing peak overlaps among Pr³⁺ intra-4f emissions and BSO host emission (i.e., Bi^{3+ 3}P₁ → ¹S₀), as well as the involved energy transfer (ET) mechanisms, were clearly distinguished for the BSO:Pr³⁺ system. A temperature-stimulated ET from the BSO host to Pr³⁺ ions was proved with greatly enhancing the entire emission intensities of Pr³⁺ to 318.19% at 428 K relative to the initial value at 298 K, and in reverse reducing that of the BSO host to 10.54% versus the case at 298 K. Such a rapid changing mode of fluorescent intensity ratio of intra-4f emissions over host emission will strategically develop the desired wide-range high-temperature luminescent thermometers.